“Everyone knows that the cost of housing varies across neighborhoods throughout the region,” says Harriet Tregoning, director of the Office of Planning. “But fewer people recognize the extent to which transportation costs vary by location and affect real affordability.”

According to the study, transportation costs can be lower if neighborhoods enable their residents to live without owning a car.

“Our years of research show that transportation costs are a significant part of a household budget—sometimes exceeding housing expenses—and those costs vary significantly depending on where a person lives,” said Peter Haas, chief research scientist for CNT. “Places that are ‘location efficient,’ which offer multiple transportation options and access to amenities, tend to have low transportation costs. This helps residents be more economically resilient, and enables them to better weather economic adversity.”

The D.C. study is based on CNT’s Housing + Transportation (H+T®) Affordability Index, a value that uses U.S. Census data to examine how neighborhood and household characteristics affect transportation costs, such as car ownership and transit use. The model was developed with the help of the Brookings Institution’s Urban Markets Initiative. Along with the help of the Rockefeller Foundation, the Index model has been applied to 337 metro regions in the United States to measure the true affordability of housing by calculating the transportation costs associated with a home’s location.

The Index does not only look at commuting to and from work to calculate transportation costs. It also includes travel that is part of the household’s daily routine. This Index includes six neighborhood variables: residential density, gross density, average block size in acres, transit connectivity index, job density and average time journey to work. There are also three household variables included in the calculation: household income, household size and commuters per household. When these nine variables are combined with car ownership, car usage and public transit usage, the ensuing value is the total transportation costs of a household.

By including these variables, the study shows how decisions in land use planning, like incorporating mixed-use and transit-oriented developments, can affect household transportation costs for a neighborhood.

The study’s findings can be helpful in attaining the goals of “Region Forward,” a report by the Greater Washington 2050, a coalition of public, business, civic and environmental leaders to improve the quality of life for Washington area residents over the next 50 years. One of Region Forward’s goals is to make sure average household housing and transportation costs in major job centers do not exceed 45 percent of the area median income.

“We are at a critical time for the region,” says Dave Robertson, executive director of the Metropolitan Washington Council of Governments. “We need to address the market pressures around our transit stations that force low-income families away from transit and develop a regional plan to channel growth around our transit investments that creates complete communities.”

Since the first phase of the H+T Index was released in January 2006, the calculations rely on data from the 2000 Census. CNT is planning to update the Index using the most recent American Community Survey data from the Census Bureau.